feat: allow using prometheus-client crate with PrometheusClientLayer (

apache#3134)

* refactor prometheus layer

* add prometheus-client to deps

* chore: simplify imports

* refactor the metrics into a trait

* feat: add implementation with prometheus-client

* fix: allow using different trait

* cargo fmt

* refactor: add a seperate layer

* fix: docs

* fix typo

* fix: cargo fmt

* add a prefix

* use structed labels

* use labels in array

* remove the unused metrics

* rename stats to metrics

* record request duration in wrapper

* fix fmt

core/Cargo.toml

@@ -83,8 +83,10 @@ layers-all = [
 layers-chaos = ["dep:rand"]
 # Enable layers metrics support
 layers-metrics = ["dep:metrics"]
-# Enable layers prometheus support
+# Enable layers prometheus support, with tikv/prometheus-rs crate
 layers-prometheus = ["dep:prometheus"]
+# Enable layers prometheus support, with prometheus-client crate
+layers-prometheus-client = ["dep:prometheus-client"]
 # Enable layers madsim support
 layers-madsim = ["dep:madsim"]
 # Enable layers minitrace support.
@@ -243,6 +245,7 @@ percent-encoding = "2"
 persy = { version = "1.4.4", optional = true }
 pin-project = "1"
 prometheus = { version = "0.13", features = ["process"], optional = true }
+prometheus-client = { version = "0.21.2", optional = true }
 prost = { version = "0.11", optional = true }
 quick-xml = { version = "0.29", features = ["serialize", "overlapped-lists"] }
 rand = { version = "0.8", optional = true }

core/src/layers/mod.rs

@@ -56,6 +56,11 @@ mod prometheus;
 #[cfg(feature = "layers-prometheus")]
 pub use self::prometheus::PrometheusLayer;
 
+#[cfg(feature = "layers-prometheus-client")]
+mod prometheus_client;
+#[cfg(feature = "layers-prometheus-client")]
+pub use self::prometheus_client::PrometheusClientLayer;
+
 mod retry;
 pub use self::retry::RetryInterceptor;
 pub use self::retry::RetryLayer;